Bifocal lenses are comprised of two or more areas, or zones, with different optical powers, including typically a far-power Optic Zone for distance vision, and a near-power Optic Zone for near or close up vision. The two zones may be subdivided into additional power zones in which case a lens may be called a multifocal lens. Previously known multifocal lenses have been limited by known manufacturing apparatus, such as, for example, cast molding, standard lathing or tooling technology, and injection molding technology.
The retinal image and the visual percept that results from it are dependent upon the light that enters an eye through the entrance pupil. In order for a bifocal contact lens to function properly, the entrance pupil must be covered at least partly or, more effectively, completely by the distance-power zone of a lens when an eye observes a distant object, and covered at least partly or, more effectively, completely by a near-power zone of a lens when an eye observes a near object. This function may be accomplished by the principle of alternating vision in which a shifting action or translation of a contact lens is made to occur in order to place one or the other zones in front of the entrance pupil as an eye alternates between viewing distance and near objects.
Alternatively, a principle known as simultaneous vision may be utilized whereby a lens is designed and fitted in such a way as to position part or all of both the far and near-power zones in front of the entrance pupil at the same time so that each contributes to the retinal image simultaneously. There is little or no translation required with this type of lens however, consequently two images are seen simultaneously, compromising vision.
Generally, the two types of conventional bifocal contact lenses are segmented and concentric. Segmented bifocal contact lenses or translating contact lenses, generally have two or more divided optical power zones. A far-power zone is usually the upper zone and a near-power zone is usually the lower zone. With such a translating lens, a far-power zone of a lens is in front of the entrance pupil of an eye in straight-ahead gaze, while in downward gaze, the add power or near-power zone of a lens is over the entrance pupil. Concentric bifocal contact lenses generally have a central power zone and one or more annular power zones that function usually, but not always, by the simultaneous vision principle. It is recognized that these lenses do not provide good vision for both distance and near viewing, and are only worn successfully by those who are willing to accept less than optimal vision.
Effective use of a bifocal contact lens requires translation of an ocular system between vision surfaces when an eye changes from gazing at an object at a distance to gazing at a nearby object. Alternatively, there may be a desire to have a translating multifocal contact lens that may have one or more intermediate-power zones in addition to far- and near-power Optic Zones. Such a translating contact lens may have to have an ability to control and optimize the amount of movement of a lens when the pupil translates from distance vision, to intermediate vision, to near vision, or any combination thereof.
While there are many designs for soft translating contact lenses, soft contact lenses have difficulty translating across the surface of an eye when the visual direction of an eye changes from a straight-ahead gaze, to a downward gaze. In one prior art example, describes a soft bifocal contact lens that has an integrally formed bevel to aid translation of a lens. While other designs may have the capability to translate across the surface of an eye when the visual direction of an eye changes from a straight-ahead gaze, to a downward gaze, but are not very efficient at controlling movement of a lens during an eye's translation to a different visual direction. Another prior art example, describes a soft multifocal contact lens that has an integrally formed ramped ridge zone adjoining an outwardly extending latitudinal ridge that sits on an eyelid to aid in translation of a lens. The latitudinal ridge portion has a bump at each end, thereby increasing elevation height of the ends of the ridge compared to the elevation height in the middle. Another disadvantage of the prior art is discomfort when worn upon an eye.
Therefore, there is a need for a soft translating multi-focal contact lens that is capable of limiting the amount of translation across the surface of an eye when an eye changes position from distance vision to near vision, and provides wearers with improved comfort. There is also a need for a soft translating multi-focal contact lens that can limit the amount of translation across the surface of an eye when an eye changes position from distance vision, to intermediate vision, to near vision and improves optical efficiency.